1. Field of the Invention
The present invention generally relates to an information processing apparatus for processing document information.
2. Description of the Related Art
Recently, it has been the case that a large amount of documents are being distributed, so that security concerns about information leakage to a third person have become higher. Therefore, when documents including confidential information are to be displayed or printed by an information processing apparatus, a user generally builds a security system and manages information under a state in which the document can be protected.
However, an electronic document may also be comparatively easy to copy and alter. Thus, security measures can be provided in the electronic document itself.
For example, there is a system which encrypts an electronic document itself, and allows only a person having a secret key to decrypt and read the document, and a system which attaches a signature file to an electronic document and does not allow a person to view or print the document when the signature file is not identical.
However, if the entire electronic document is subjected to security measures, a user may need to edit or re-encrypt the electronic document if the user wants to protect only a part of the document and disclose the remainder of the document. Further, in the case where a signature file is attached, the signature may have to be re-attached if the document is edited, which may take time and effort.
Further, as printer performance is improved, a direct print system is increasingly being used, by which an electronic document is directly sent to a printer and printed as it is.
However, currently, there are few printers having the performance and specifications to handle a signature file and an encryption key system. Thus, many printers print out documents without regard to the functions of the signature file and the encryption key system provided in the document, so that confidential data may be leaked by output to a medium as a paper, even though the data is protected as the electronic document.
In terms of protecting confidential information, editing an electronic document itself may be the most effective. For example, Japanese Patent Application Laid-Open No. 2002-259363 describes a technique which extracts a confidential information part in a file and replaces the part with another character not existing in the file, e.g., an alphabet and an initial character.
However, when the confidential information part is replaced with the other character, the original data cannot be restored. Thus, Japanese Patent Application Laid-Open No. 2007-156861 describes a method which can restore a replaced document to an original document by generating a conversion table with a character to replace the document. This method may be capable of replacing only confidential information to be protected, and thus can easily disclose the non-confidential parts to public.
However, in this method, a manager may have to manage the conversion table. Thus, when there are a lot of confidential documents, a conversion table may be generated for each of the confidential documents, so that the management of the conversion tables may become complicated.
Further, if the same conversion table is used for each document in order to avoid the complicated management, it may occur that if one document is analyzed, the result may be inadvertently applied to every other document.
Further, when an electronic document is replaced with a character not existing in the document, every character in the entire document may have to be checked. Since it can be common for an electronic document to have several hundreds or thousands of pages, it may take an excessive amount of time to generate a conversion table. Furthermore, it can occur that the conversion table is not properly generated if almost all characters already exist in the electronic document.